(a) Technical Field
The present invention relates to a corrugated plastic composite spring for a vehicle suspension. More particularly, it relates to a plastic composite spring for a vehicle suspension and an apparatus and method for manufacturing the corrugated plastic composite spring, which can substitute for a typical metal coil-type spring.
(b) Background Art
Generally, a vehicle's body is supported by a suspension connected to tires. The suspension absorbs vibration and shock generated during driving of a vehicle to provide a comfortable ride feeling, and serves to control overall balance of the vehicle body in accordance with the conditions of the road surface. Also, the suspension enables stable handling of a driver against a centrifugal force generated during turning of a vehicle, and prevents a vehicle from tilting in one direction due to the centrifugal force.
Suspensions are classified into leaf springs with stacked steel plates and coil springs with a helical steel wire. The leaf springs and coil springs are typically formed of metal materials. Recently, in order to overcome reduction of chipping resistance due to corrosion and achieve reduction of vehicle weight, many studies have been conducted to substitute metal materials with plastic composites.
Since leaf springs have a relatively simple planar structure, leaf springs have already been substituted with plastic composites. However, in the case of the coil springs, when metal materials are simply substituted with plastic composites, it is difficult to implement a spring constant which is high enough to be applied to vehicle suspensions due to a stiffness difference between a metal and a plastic composite.
Although the spring constant can be somewhat implemented by increasing the wire diameter and width and using a high-stiffness material while maintaining the helical shape, increases in the weight and material cost are hindering the mass-production of coil springs using high-stiffness materials so far.
Accordingly, in order to substitute for metal coil-type springs using high-stiffness materials, studies on various plastic composite springs having coiled, waved, and corrugated shapes have resulted. Among them, plastic composite springs having corrugated shapes are most advantageous for implementation of a desired spring constants due to their closed-sectional structures.
A technology related to a corrugated plastic composite spring is disclosed in U.S. Pat. No. 4,235,427. However, since it has to be manufactured into a closed sectional structure using high-stiffness material to implement a spring constant high enough to be applied to a vehicle suspension, the formation process is difficult, and the productivity is low, making its mass-production difficult. Also, since the technology includes a hand lay-up process and a filament winding process that are high-priced processes, there are limitations in substituting for a typical metal coil-type spring.
Although a method for manufacturing a corrugated plastic composite spring has been proposed using a typical blow molding process, materials used for production of the corrugated plastic composite spring are limited to plastic composites containing at least a certain amount of strength-reinforcing material, or pure thermoplastic resin. It is difficult to implement a spring constant and durability enough to be applied to a vehicle.
Also, in the typical manufacturing methods described above, since corrugated plastic composite springs can be manufactured by only using a single material, it is difficult to secure enough isolation performance against vibration and noise. This leads to reduction of Noise, Vibration, and Harshness (NVH) characteristics.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.